Custom Linq Ordering

问题

I have over a thousand folders, each folder contains one or more files with the following names:

Unordered:

Alison.ext
Heather.ext
Molly.ext
Paula.ext
Sam.ext

Ordered:

Molly.ext
Sam.ext
Heather.ext
Alison.ext
Paula.ext

I would like to write an expression to sort this list as described above.

回答1:

//Creating a dictionary with the custom order
var order = "MSHAP";
var orderDict = order.Select((c,i)=>new {Letter=c, Order=i})
                     .ToDictionary(o => o.Letter, o => o.Order);

var list = new List<string>{"A.ext", "H.ext", "M.ext", "P.ext", "S.ext"};

//Ordering by the custom criteria
var result = list.OrderBy(item => orderDict[item[0]]);

Instead of calling orderDict[item[0]] you could have a nice helper method that cares for the fringe cases (non existent letters, null, and so on). But that's the idea.

回答2:

Here's a method that produces keys for ordering

public int OrderKey(string fileName)
{
  char first = fileName[0];
  int result =
     first  == 'M' ? 1 :
     first  == 'S' ? 2 :
     first  == 'H' ? 3 :
     first  == 'A' ? 4 :
     first  == 'P' ? 5 :
     6;
  return result;
}

Here's how to call it:

List<File> ordered = Files.OrderBy(f => OrderKey(f.FileName)).ToList();

回答3:

List<char> sortKeys = new List<char> { 'M', 'S', 'H', 'A', 'P' };
sortKeys.Reverse();
List<FileInfo> files = new List<FileInfo>(6);

foreach(char sortKey in sortKeys)
{
    var topFiles = files.Where(file => file.Name.StartsWith(sortKey.ToString()));
    var remainingFiles = files.Except(topFiles);
    files = topFiles.Concat(remainingFiles).ToList();
}

Untested and I'm sure there are faster ways, but at least it's with linq stuff as you asked :-)

edit: I just saw the edit on your post and now I don't have any idea anymore what you really want to do, so my code is probably useless to you..

回答4:

You didn't mention exactly what sort of objects you have in the list, but let's say it's some generic arrangement like so:

public class File {
  public string FileName { ... }
  public long FileSize { ... }
  /* elided */
}

Then, given an IEnumerable called, say, files, you can just do:

var result = files.OrderBy(f => f.FileName);

回答5:

You can store the desired order list in an array

int[] iIndex = {3,2,0,4, 1};

Say str holds your unordered List

List<string> str = new List<string>();
str.Add("Alison.ext");
str.Add("Heather.ext");
.
.
.

Add your list and corresponding order into a datatable

DataTable dt = new DataTable();
                dt.Columns.Add("Order", typeof(Int32));
                dt.Columns.Add("Name");

                for (int iCount =0; iCount< str.Count ; iCount ++)
                { 
                    DataRow drow1 = dt.NewRow();
                    drow1[0] = iIndex[iCount];
                    drow1[1] = str[iCount];
                    dt.Rows.Add(drow1);

                }
                dt.AcceptChanges();

Fynally Order yuor list to get yuor expected list

 var result = from ls in dt.AsEnumerable()
                         orderby ls.Field<int>("Order")
                         select ls;      

来源：https://stackoverflow.com/questions/942039/custom-linq-ordering